A computer network is a collection of interconnected computing devices that exchange data and share resources. In a packet-based network the computing devices communicate data by dividing the data into small blocks called packets. Certain devices within the network, such as routers, maintain routing information that describes routes through the network. In this way, the packets may be individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
Examples of computer networks include enterprise networks, branch networks, service provider networks, home networks, virtual private networks (VPNs), local area network (LANs), virtual LANs (VLANs) and the like. In any case, the computer networks may enable remotely located sources and receivers to share data. In some cases, the computer network may be configured to support multicast traffic, such as Internet Protocol Television (IPTV), desktop conferences, corporate broadcasts, music and video web casts, and other forms of multimedia content. As an example, the computer network may utilize protocol independent multicast (PIM) as a multicast routing protocol to control delivery of multicast traffic from sources to receivers or subscriber devices for particular multicast groups. PIM may operate in several different modes, including Dense Mode (DM), Sparse Mode (SM), Source-Specific Mode (SSM), and Bidirectional Mode (BIDIR).
PIM-SM is a multicast routing protocol that can use the underlying unicast routing information base or a separate multicast-capable routing information base. Routers within computer networks utilizing PIM-SM typically build unidirectional trees rooted at a central node, referred to as a Rendezvous Point (RP), per multicast group, and optionally create shortest-path trees per multicast source group combination. Further details regarding PIM-SM can be found in W. Fenner, et al., “Protocol Independent Multicast-Sparse Mode (PIM-SM),” RFC 4601, August 2006, the entire content of which is incorporated by reference herein.
In many environments, PIM-SM and other multicast routing protocols are used to control delivery of multicast traffic within shared media networks (e.g., local area networks) (LANs), such as Ethernet networks. Unlike point-to-point transit links, shared media networks can introduce several complications to multicast communications, such as duplicate copies of multicast traffic appearing on the LAN by multiple upstream routers. PIM seeks to address these issues by performing an election of a single router for forwarding the multicast traffic. That is, a single router is elected to forward multicast traffic to a shared media LAN, thereby seeking to prevent duplicate data packets from appearing on the LAN from different routers. Conventionally, this election is performed using the PIM protocol upon detecting duplicate multicast traffic within the LAN. According to this “data driven” technique, upon detecting the presence of the duplicate multicast traffic, routers capable of sourcing the multicast traffic into the LAN exchange PIM Assert messages and ultimately elect an “assert winner” as the router for forwarding the multicast traffic. Control plane-driven assert mechanisms for PIM have been recently mentioned in industry. However, initial work in this area still suffers from many shortcomings in many real-world deployment scenarios.